also, the flip kit I bought comes with a piece that creates a flat surface between the axle and the leafs.

This is extremely important, otherwise the axle can "twist" under load. I worked with a guy that flipped his mini truck axle and leafs like you are saying and after only a couple of days of driving he ended up twisting the axle (relative to the springs) and it pulled the driveshaft out and broke the u joint and alot of other damage. It happened when he accelerated hard onto the freeway.